1. Field of the Invention
The present invention relates to supercalenders of the type wherein the rolls are adapted for limited separation from one another in one mode and are in calendering nipping engagement with one another in another mode.
2. Description of the Prior Art
Supercalenders with which the present invention is concerned are well known in the art and comprise a substantial stack of calender rolls wherein separation of the rolls may be controlled either from the top or the bottom of the stack. Where control is from the bottom of the stack, a king roll at the bottom of the stack is moveable between a lowered position and a raised position. In the lowered position of the king roll, a substantial number of calender rolls thereabove separate from one another to provide gaps therebetween to facilitate threading a new web of material through the stack or to relieve any damaging effect of broke or creased web passing through the roll nips. As thus gapped, the opposite ends of the rolls are supported by their bearing structures on shoulders along upright suspension spindles at the opposite sides of the stack. In the calendering mode of the stack, the king roll acting through the next adjacent calendering roll pushes all of the rolls thereabove into nipping relation, wherein the bearing structures for the rolls are lifted from the spindle shoulders. For uniform nip loading, the topmost roll in the stack may be hydraulically biased downwardly. Calenders of the type just described are represented in U.S. Pat. Nos. 3,364,848, 3,369,483, 4,290,351 and 4,311,091.
Inasmuch as the calender rolls are quite heavy, such, for instance as about 42,000 pounds each in a supercalender, their bearing structures must be fairly massive to afford adequate support when the rolls are individually supported on the spindles. Typically each bearing structure at each end of each of the rolls may weigh from 4,000 to 5,000 pounds. Therefore, when the rolls are lifted to the nipping, calendering mode, and the bearing structures are in deadweight relation at each end of each roll, the deadweight end loads on the rolls tend to distort the rolls and thus distort nips between rolls from the ideal straight line. This distortion or warping condition is aggravated where, as is often desirable, fly rolls (i.e. guide rolls) are supported on the housings of the bearing structures.